Method for making irregular shaped single crystal particles and the use thereof in anodes for electrochemical cells

Abstract

A method for making single crystals of metal or other crystallizing materials whereby powders of irregular shaped single crystal particles (as small as 325 mesh or about 50 microns) may be readily and economically made. Said method comprises the steps of: (a) forming thin individual coatings on each of said particles such as oxides of metals on metal particles; (b) melting the particle material within said coatings which function as individual particle crucibles; (c) cooling the melted particles within the coatings to form individual single crystals each within its own coating: and (d) removing the coating such as by solvation with a solvent or by chemical reaction. The single crystal particles conform to the original shape of the particles which may be irregular. Such irregular shaped single crystals, such as of zinc, when used in electrochemical cell anodes enables the utilization of reduced amounts of mercury for amalgamation thereof without significant increase in cell gassing.

What is claimed is: 
     
       1. A method for making single crystal metal particles comprising the steps of: (a) forming individual substantially continuous coatings on the external surfaces of each of the individual particles of a particulate metal material which is capable of being crystallized, said coatings being of a material having higher melting and decomposition temperatures than the melting temperature of said particulate metal material and wherein said coatings are each of a thickness and composition with sufficient mechanical strength to act as self-supporting shape retaining crucibles for said metal particles when such metal particles are melted;   (b) raising the temperature of said coated particulate metal material to above the melting point thereof but below the lower of the melting point or the decomposition temperature of said coating material whereby substantially all of the particulate metal material is melted within said coating; and   (c) slowly cooling said particulate metal material whereby substantially all of said particles become individual single metal crystals.   
     
     
       2. The method of claim 1 wherein said coatings are each removed without substantially disrupting said single crystals. 
     
     
       3. The method of claim 1 wherein said coatings are each about 1 micron thick. 
     
     
       4. The method of claim 1 wherein said single crystal particles are of an irregular shape. 
     
     
       5. The method of claim 1 wherein the particulate metal material has a particle size between about 50 and 500 microns. 
     
     
       6. The method of claim 1 wherein said particulate metal material is melted in a non-reactive environment. 
     
     
       7. The method of claim 1 wherein said particulate metal material is comprised of particles of irregular shape and said single crystals are of substantially corresponding irregular shape. 
     
     
       8. The method of claim 1 wherein said coating material is an oxide of said metal material. 
     
     
       9. The method of claim 8 wherein said coating material is formed on said metal particles by heating said metal particles in the presence of an oxidant at an elevated temperature below the melting point of said metal. 
     
     
       10. The method of claim 9 wherein said metal is zinc and said elevated temperature is between 370° C. to 400° C. 
     
     
       11. The method of claim 8 wherein said metals are selected from the group consisting of aluminum, cadmium, lead, lithium, magnesium, potassium, rubidium, sodium, tin and zinc. 
     
     
       12. The method of claim 11 wherein said metal is zinc. 
     
     
       13. The method of claim 12 wherein the removal of said oxide coating is effected by solvation thereof.